Miniature belt grinder



Feb. 18, 1969 A, EDMAN 3,427,757

MINIATURE BELT GRINDER Filed Feb. 17, 1967 Sheet L of 2 Feb. 18, 1969 R. A. REDMAN 3,427,757

MINIATURE BELT GRINDER Filed Feb. 17, 1967 Sheet 2, of 2 I t r ATTORNEYS United States Patent 3,427,757 MINIATURE BELT GRINDER Richard A. Redman, 916 Oneida St., Lewiston, N.Y. 14092 Filed Feb. 17, 1967, Ser. No. 616,949 US. Cl. 51-170 9 Claims Int. Cl. B24b 23/00, 21/00 ABSTRACT OF THE DISCLOSURE Brief summary and background of the invention The invention is of the hand tool type of grinders and is particularly adapted for use in connection with small cavities or restricted openings in sheet metal, castings,

forgings and the like for deburring and smooth finishing. A

The grinders in use are ordinarily of relatively massive construction, whereas the present invention has a thin, elongated grinding area which enables it to get into tiny or confined spaces and successfully finish or polish surfaces where only a restricted access opening is available.

The grinding is accomplished, either where the belt passes over a small pulley, or along the sides of a thin arm by an endless belt which is automatically kept in a tensioned state by means which also cooperates in permitting a ready change of belts to permit utilization of bolts of varying lengths and varied abrasive surfaces. A safety factor in the event of belt breakage is provided along with many other features not present in the prior art,

In the drawing:

FIG. 1 is a side view of the tool;

FIG. 2 is a top view;

FIG. 3 is a front view;

FIG. 4 is a rear view;

FIG. 5 is a partial side section of the abrasive belt, and its mounting structure;

FIG. 6 is an exploded side section of a belt mounting arm extension, its connection to the main arm and its pulley and support for the pulley; and

FIG. 7 is a view :partly in section taken on line 77 of FIG. 6.

Referring now to the drawings in greater detail, the tool has a casing 10 in which is mounted a suitable electric motor 12; the casing having a pistol type grip portion 14 and a trigger type electrical switch 16. Conventional wiring connects the tool to an electrical power source and the trigger switch to the motor whereby contraction of the operators finger on trigger 16 will complete an electrical circuit and operate the motor.

Motor 12 has shaft 18 on the end of which is fixedly mounted a belt driving pulley 20, which pulley has a longitudinal axis of rotation.

The top of casing 10 is provided with an opening having edges 22 which taper providing a smaller opening at the top front than at the top rear. The edges 22 continue downward at the rear edges 23 and widen out to permit access at the rear of the casing.

An elongate arm 24 is positioned in the casing beneath the opening defined by the edges 22, and is supported therein by a pivot pin 26 which has its ends mounted in lugs which are part of the casing. The rear end of arm 24 is continually urged upwardly by a spring such as coil spring 28 which is suitably mounted between the bottom of the arm and a portion of the casing. Near the rear of arm 24 it is provided with an opening 30 to support a transversely disposed axle 32 which carries a pair of idler belt supporting pulleys 34, one pulley being mounted on each side of arm 24. The rear end of arm 24 terminates in a hand or thumb press lever extension 36.

As most clearly shown in FIGS. 5 and 6, the front end of arm 24 is provided with an opening 38, a screw threaded hole 40 and a set screw 42. Opening 38 is intended to detachably receive the shank 44 of an elongated grinding arm extension 46 which would be held in place by the set screw 42. The free end of arm extension 46 has extending from its lower side a pulley supporting portion 48 having beveled bottom edges 50. A boss 52 formed on the upper side of portion 48 is internally threaded to receive the enlarged threaded end 54 of a vertically disposed pulley axle 56.

An idler belt supporting pulley 58, having suitable bearings 60 is provided with a bottom opening 62 of sufiicient diameter to freely slide over boss 52 with a hub opening 64 fitting over axle 56. The top of axle 56 may be headed at 57 to retain the pulley at its axle, and the bottom of the axle may be slotted to permit tightening and loosening the same. Pulley 58 may be rubber covered as shown at 66 if desired, and sufiicient space 68 is provided between the periphery of pulley 58 and the adjacent end of extension arm 46 so that pulleys of different diameter may be used.

Platen strips 70 may be secured by adhesive or other suitable means to each side of extension arm 46.

An endless abrasive belt 72 is entrained around pulleys 20, 34 and 58 by placing the belt first around pulley 26 and then over the top of the pair of pulleys 34. The belt is then strung along toward the front, and on each side, of arm 24 by sliding the belt semi-edgewise down into the space between the sides of arm 24 and the casing top opening edges 22. By pressing downwardly and inwardly on the thumb extension 36, the arm 24 and extension 46 can be tilted to the dot-dash line position shown in FIG. 5 with the pulleys 24 being brought closer to pulley 20 permitting the outer end of the belt loop to be slid down over pulley 58. Upon release of pressure on 36, spring 28 raises the rear of arm 24 and pulleys 34 and tightens belt 72. During use, as the belt stretches the spring 28 will continue to raise pulleys 34 and maintain working tension in the belt.

To remove a belt, pressure on the thumb press lever extension 36 will slacken the belt and permit easy removal and replacement.

It will be seen that different lengths of extension arms 46, and different diameter pulleys 58 can readily be used, whenever the depths and sizes of surfaces to be ground dictate.

It should also be noted that the edges 22 of the casing top opening overhang the belt edges to a slight distance, which acts as a safeguard in the event of a belt break.

The beveled edges 50 of the support for pulley 58 prevent fraying of the lower edge of the belt and also minimize harmful contact with a work piece, while the twisting of the belt assists in proper tracking of the same.

The invention provides a semi-circular grinding surface as the belt passes around the surface of pulley 58 and also flat grinding areas on each side of the arm extension 46.

While the invention has been described in a certain specific form by way of illustration, the invention is not so limited, as modifications and changes can readily be made therein without departing from the spirit and scope thereof as defined in the appended claims.

What I claim as my invention is:

1. A hand tool grinding device having an endless abrasive surfaced belt powered by an electric motor, a plurality of pulleys for supporting said belt, and a casing including a hand grip and a switch for supporting and enclosing said motor and a portion of said belt, the improvement consisting of:

a belt driving pulley attached to said motor and having its axis of rotation extending longitudinally in said casing,

a pair of spaced belt supporting pulleys having their axis of rotation extending transversely in said casing,

a belt supporting pulley mounted externally of said casing, with its axis of rotation extending vertically with respect to said casing,

said belt being entrained around all of said pulleys,

and resilient means mounted in said casing for maintaining tension in said belt and permitting easy removal and replacement of said belt.

2. The grinding device of claim 1 wherein an elongate arm pivoted in said casing supports said pair of spaced belt supporting pulleys and said externally mounted pulley.

3. The grinding device of claim 2 wherein said resilient means acts between said casing and said arm.

4. The grinding device of claim 3 wherein the arm at one end terminates in a thumb press extension, whereby manual pressure on said extension decreases the distance between the belt driving pulley and the pair of spaced belt supporting pulleys to permit removal and replacement of a belt.

5. The grinding device of claim 4 wherein said arm is made in sections to permit use of varying length sections to support said externally mounted pulley.

6. The grinding device of claim 5 wherin said arm section supporting the externally mounted pulley is provided on each side with platens for backing up the belt.

7. The grinding device of claim 6 wherein the casing has edges overlying a portion of the side edges of the belt to provide a safeguard in the event of belt breakage.

8. A hand tool grinding device having an endless abrasive surfaced belt powered by an electric motor, a plurality of pulleys for supporting said belt, and a casing including a hand grip and a switch for supporting and enclosing said motor and a portion of said belt, the improvement consisting of:

a belt driving pulley attached to said motor and having its axis of rotation extending longitudinally in said casing,

an elongate arm mounted in said casing and projecting longitudinally from said casing,

a belt supporting pulley mounted on the free end of said arm with its axis of rotation extending vertically with respect to the casing,

pulley means mounted adjacent said belt driving pulley, with its axis of rotation extending transversely of said casing,

said belt being trained about said belt driving pulley and said belt supporting pulley and passing over said pulley means between said belt driving and said belt supporting pulleys to cause said belt to straddle that portion of the arm projecting from said casing,

and resilient means for tensioning said belt.

9. The grinding device of claim 8 wherein said arm is pivotally mounted in said casing, said pulley means being mounted on said arm in said casing, and said resilient means acting between said casing and said arm.

References Cited UNITED STATES PATENTS 2,647,350 8/1953 Blazek 51-170 2,976,652 3/1961 Bedortha et a1. 51l70 2,429,647 10/1947 Randolph 51361 2,148,627 2/1939 Kulp et a1. 51-170 JAMES L. JONES, J 11., Primary Examiner. 

